1. Field of the Invention
The present invention relates to a hydrodynamic machine, especially a hydrodynamic retarder, comprising two blade wheels which are opposite of one another in such a way that they jointly form a toroidal working chamber which can be filled with a working medium in order to hydrodynamically transfer torque by way of a cycle flow of the working medium in the working chamber from the first blade wheel to the second blade wheel, wherein the first blade wheel rotates about a rotational axis and the second blade wheel rotates about the same rotational axis in the same direction of rotation or opposite of the direction of rotation of the first blade wheel, or is held in a stationary manner, and the blades of each blade wheel extend in an arc from a radially inner blade end on a radially inner wall of the working chamber to a radially outer blade end on a radially outer wall of the working chamber.
2. Description of the Related Art
Hydrodynamic machines comprise at least two bladed wheels, which will be referred to below as blade wheels and which jointly form a toroidal working chamber. One distinguishes between such hydrodynamic machines which comprise precisely two blade wheels for forming the working chamber, namely hydrodynamic couplings and hydrodynamic retarders, and such hydrodynamic machines in which additionally fixed or fixable guide blade assemblies are provided in the working chamber, so-called hydrodynamic converters. The present invention relates especially to the former hydrodynamic machines with precisely two blade wheels, and especially to hydrodynamic retarders in which drive power or torque is transferred from a first revolving blade wheel to a second fixed blade wheel or from a first revolving blade wheel to a second blade wheel revolving in the opposite direction in relation to the first blade wheel in order to brake the first blade wheel.
In vehicle drive trains in which the present invention is applicable, such hydrodynamic machines, and hydrodynamic retarders in particular, are widely used which comprise two blade wheels with blades having a planar blade profile and are opposite of each other in the axial direction in order to form the toroidal working chamber. The mutually facing free axial ends of the blades, which are also known as front edges of the blade, are usually straight and extend in the radial direction of the respective blade wheel. In order to amplify power transmission in a direction of rotation of the hydrodynamic machine, it is further proposed to provide the blade wheels with an oblique blading, such that the blades are arranged in the aforementioned direction of rotation in a piercing manner with respect to each other. This does not change anything in respect of the straight progression of the front edges of the blade in the radial direction of the blade wheel. It has further already been proposed to arrange the blades in a twisted fashion in order to integrally produce the blade wheel by way of casting in a manner so that the same can rotationally be demolded. The straight progression of the front edges of the blade in the direction of the blade wheel will not be affected thereby.
U.S. Pat. No. 5,147,181 describes a blade profile which differs completely from the one described above. In this case, the blades extend in an arc from a radially inner wall of the toroidal working chamber up to a radially outer wall of the working chamber. In accordance with this specification, it is relevant for the guidance of the flow of the hydrodynamic cycle flow in the working chamber that the arc is provided with a very specific parabolic shape.
The published patent application DE 2 239 562 A describes a hydrodynamic brake with similar arc-shaped blades, which comprise circular intersecting lines between the inside surfaces of the blades and the inside surface of the cycle shell in a top view obliquely on the plane of the separating gap between the two blade wheels. The arc of the blades has the shape of an ellipse in a view in the direction of the rotational axis on the blade wheel.
Document U.S. Pat. No. 2,126,751 A describes linear front edges of the blades which are inclined relative to the radial direction on the one hand and front edges of the blade on the other hand which have a slight arc shape in a top view of the plane of the separating gap. Respective shapes of blades are also shown by the document GB 663 463 A. U.S. Pat. No. 2,889,013 A proposes the provision of cup-shaped blades in form of hollow spherical segments.
Although hydrodynamic machines with a large variety of blade profiles are known, there is a continued need to achieve an optimum concerning the efficiency in combination with low production costs and high reliability. A further important feature is the progression of the efficiency over various speeds or at different degrees of filling (filling states in operation between full filling and minimum filling) of the working chamber.
The present invention is based on the object of providing, and what is needed in the art is, a hydrodynamic machine, especially a hydrodynamic retarder, which fulfills the mentioned requirements even better than previously known embodiments. In particular, high efficiency is to be achieved in combination with potential cost-effective production of the hydrodynamic machine or the hydrodynamic retarder, which occurs advantageously with a favorable progression of the efficiency at different speeds and different filling states of the working chamber.